During the drilling of oil and/or gas wells, a drill bit at the end of a rotating drill string, or at the end of a drill motor, is used to penetrate through geologic formations. During this operation, drilling mud is circulated through the drill string, out of the bit, and returned to the surface via the annular space between the drill pipe and the formation. Drilling mud serves numerous functions, including: cooling and lubricating the drill string and drill bit; counterbalancing the pressures encountered in the formation using hydrostatic pressure; providing a washing action to remove the formation cuttings from the wellbore; and, forming a friction reducing wall cake between the drill string and the wellbore.
During drilling, the drill string may develop unacceptable rotational torque or, in the worst case, become stuck. When this happens, the drill string cannot be raised, lowered, or rotated. Common factors leading to this situation include: (1) cuttings or slough buildup in the borehole; (2) an undergauge borehole; (3) irregular borehole development embedding a section of the drill pipe into the drilling mud wall cake; and, (4) unexpected differential formation pressure.
Differential pressure sticking occurs when the drill pipe becomes imbedded in the wall mud cake opposite a permeable zone. The difference between (a) the hydrostatic pressure in the drill pipe, and (b) the formation pressure holds the pipe in place, resulting in sticking pipe.
Differential sticking may be prevented, and a stuck drill bit may be freed, using an oil/mud or an oil or water based surfactant composition. Such a composition reduces friction, permeates drilling mud wall cake, destroys binding wall cake, and reduces differential pressure. Unfortunately, many of such compositions are toxic to marine life.
Synthetic polyalphaolefins are non-toxic and effective in marine environments when used as lubricants, ROP enhancers, and/or spotting fluid additives for water-based drilling muds. A continuing need exists for other non-toxic additives for water-based drilling muds which serve as lubricants, ROP enhancers, and/or spotting fluids.